ΔF = ±2 transitions in the hyperfine spectrum of Er I

The occurrence of 15ΔF=±2 transitions in the hyperfine spectrum of five lines of Er I was observed by means of high-resolution laser-atomic-beam spectroscopy. These normally forbidden transitions are caused by an external magnetic field which mixes closely lying hyperfine levels that have neighbouringF quantum numbers. If the Zeeman splittings under the applied magnetic field are small compared to the hyperfine splittings, the intensities of theΔF=±2 components are proportional to the square of the magnetic field strength. Under the variation of the laser intensity theΔF=±2 transitions show the same behaviour as homogeneously broadenedΔF=0, ±1 transitions. The relative intensities between theΔF=±2 components as well as the intensity ratios of theΔF=±2 to neighbouringΔF=±1 components are studied and interpreted in terms of first order perturbation theory.